DIY 053 Vapor Lock (05/27/2025)

[59lincolnrag]

Rev A (05/28/2025) re-write paragraph two for clarity and added information.
Rev B (06/01/2025) Added a company called Design Engineering, Inc.


Vapor Lock

Vapor lock happens when your fuel boils in your carburetor or your fuel line. Vaporized fuel creates back pressure in your fuel system and prevents gas from getting to your engine. It commonly occurs when a car has been idling or has been turned off and then back on. This problem has really increased with modern fuels designed for fuel-injected engines and electric fuel pumps. Its boiling point is much lower than fuel blends of the past, and it’s more volatile.

My Lincoln has a mechanical fuel pump and a 4-barrel carburetor and runs fine. Once it’s shut off, however, it cranks fine but won’t restart. After sitting for an hour or two, it will start again and run with no apparent problems. To confirm a vapor lock problem, you can install a clear hose from the fuel pump to the carburetor inlet. This will allow you to see the hose filling with fuel, with no air bubbles present. Once the engine compartment heats up, though, the fuel starts to boil and air bubbles form. In testing with an outdoor temperature of 70 degrees, the temperature of the line reaches about 120 degrees. Unfortunately, modern fuel blends can boil at temps as low as 100 degrees.

There are several ways to solve vapor lock problems, including installing an electric fuel pump, adding a plastic carb spacer and adding an insulating spacer or double gasket at the fuel pump. This can also be accomplished by using the Three-Port pump like on the later model Lincolns. You can install a fuel pump and a third return line by using a three- port fuel filter that can do the same thing. Such as a Wix 33040 (5/16) or 33041 (3/8) both have a built in 1/4" return port (orifice). This port must be "up" and return line to the tank. So, a return system will give the boiling fuel a place to go and relieve the pressure by keeping the fuel system cool by circulating through the system. A system without a return line will keep fuel in the feed line and allow it to soak up excess heat and vapor lock. When routing fuel lines keep them as far away from heat as posable. In fact some insulating material will help.

There is a company called Design Engineering, Inc. They make all types of heat insulating products.
Such as https://www.designengineering.com/vapor ... -i-d-x-36/
I am not affiliated in any way. found it doing some research.

You will need to do your own research to find out what is best for your vehicle.

Find a gas station near you that provides ethanol-free blends. Ethanol blends, with their lower boiling point, are some of the major culprits causing vapor lock problems.